Multiple-antenna system for cell-specific and user-specific transmission

ABSTRACT

A reception method and apparatus for use in a multi-cell orthogonal frequency division multiple access (OFDMA) wireless system. In a unicast receive mode during a first receive time period, a first group of orthogonal frequency division multiplexing (OFDM) symbols is received by a mobile device from multiple of a plurality of antennas at a serving base station. In a single-frequency-network (SFN) receive mode during a second receive time period, a second group of OFDM symbols is received by the mobile device from one of a plurality of antennas at the serving base station. The transition between the first receive time period and the second receive time period occurs during a cyclic prefix or a cyclic postfix between OFDM symbols, and the plurality of antennas produce a first beam pattern during the unicast receive mode and a second beam pattern during the SFN receive mode.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of U.S. patentapplication Ser. No. 14/725,254 (now U.S. Pat. No. 9,344,313), filed May29, 2015, which is a continuation application of U.S. patent applicationSer. No. 13/668,102 (now U.S. Pat. No. 9,048,540), filed Nov. 2, 2012,which is a continuation application of U.S. patent application Ser. No.13/396,487 (now U.S. Pat. No. 8,326,366), filed Feb. 14, 2012, which isa continuation application of U.S. patent application Ser. No.13/276,240 (now U.S. Pat. No. 8,116,822), filed Oct. 18, 2011, which isa continuation application of U.S. patent application Ser. No.11/908,262 (now U.S. Pat. No. 8,041,395), having a 371 date of Oct. 30,2008, which is a national stage application of International ApplicationNo. PCT/US06/60888, filed Nov. 14, 2006, which claims the benefit ofU.S. Provisional Patent Application No. 60/736,500, filed on Nov. 14,2005. U.S. patent application Ser. Nos. 13/396,487, 13/276,240 and11/908,262 are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The disclosed embodiments relate, in general, to wireless communicationand, in particular, to antenna systems for use in cellular communicationand broadcasting.

BACKGROUND

An antenna system is an indispensable component of any wirelesscommunication network. Wireless communications is presently available inmany forms, among which the most common one is cellular/mobilecommunications.

In a cellular wireless network, the geographical region to be servicedby the network is normally divided into smaller areas called cells.Within each cell are mobile stations (MSs) that are used by users toaccess the network. A cell may be further divided into multiple sectorsand in each sector the coverage is provided by a base station (BS). A BSalso serves as a focal point to distribute information to and collectinformation from MSs that are located in the cell by radio signals thatare transmitted by the BS antenna.

There are different types of transmissions carried out by BSs. A BS cansend specific data to an individual MS within its sector; a BS may alsosend a set of common data to all the MSs with its sector; a BS may alsosend data via a common channel to all the MSs within a cell; and a groupof BSs may broadcast information via a common channel simultaneously toall MSs within a group of cells. Depending on the type of transmission,a distinctive set of requirements may be required for the BS antennasystem in terms of radiation patterns, power settings, etc. In addition,a frequency-reuse scheme may impose constraints on the antenna system.The extent to which an antenna system meets the wide range ofrequirements and constraints directly impacts on the wireless networkperformance. Therefore, there is a need to create an antenna system thatis reconfigurable, adjustable, and controllable to enable a BS to carryout transmissions from a type of application to the other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the coverage of a wireless communication network thatis comprised of a plurality of cells.

FIG. 2 is a block diagram of a receiver and a transmitter, such as mightbe used in a multi-carrier wireless communication network.

FIG. 3 is a graphical depiction of a multi-carrier signal structure inthe time domain.

FIG. 4 is a block diagram of a particular realization of a transmitterfor cellular communication and broadcast.

FIG. 5 is a block diagram of a variant realization of a transmitter forcellular communication and broadcast.

FIG. 6 is a block diagram of a distribution network used in atransmitter for cellular communication and broadcast.

FIGS. 7A and 7B are block diagrams of alternate implementations of thedistribution network.

FIG. 8 is a graphical depiction of using different types of antennabeams for different types of transmissions.

FIG. 9 is a graphical depiction of using a conformed elevation beam forunicast and sector-specific broadcast and an extended elevation beam forbroadcast.

FIGS. 10A and 10B are perspective views of examples of antenna systems.

FIG. 11 is a block diagram of a beamforming process in an OFDMA system.

FIG. 12 is a perspective view of an antenna that generates differentelevation beams.

FIG. 13 is a block diagram of a bank of N distribution networks used inbeamforming, transmit-diversity, or MIMO applications.

FIG. 14 is a graphical depiction of inserting a transition periodbetween a video broadcast slot and a data unicast slot.

DETAILED DESCRIPTION

A multiple-antenna system for cellular communication and broadcasting isdisclosed. The multiple-antenna system can be controlled, adjusted,configured, or reconfigured to produce desirable radiation beam patternssuitable for different types of applications (e.g., voice, data, video,etc.). For example, the multiple-antenna system can be controlled toenable unicast transmissions with a specific reuse scheme or broadcasttransmissions with one or more channels.

In some embodiments, a signal distribution network is provided in themultiple-antenna system. The signal distribution network is embedded ina transmitter at a base station (BS) and controls the distribution ofsignals to one or more antennas. Various antenna radiation patternssuitable for different applications can be generated by reconfiguringthe connections and gain settings in the signal distribution network. Byshaping the azimuth pattern of a beam and activating appropriate antennaelements to produce a predefined elevation pattern of a beam, differentradiation beam patterns may be generated for use in different types ofapplications. For example, narrow beams may be generated for use inunicast applications, whereas sector beams may be generated for use inbroadcast applications.

In some embodiments, certain techniques are employed to manage thetransition from one type of transmission mode to another type oftransmission mode. A transmission mode may correspond to a particularantenna beam pattern or to other settings for a particular application.

The following discussion contemplates the application of the disclosedtechnology to a multi-carrier system, such as Orthogonal FrequencyDivision Multiplexing (OFDM), Orthogonal Frequency Division MultipleAccess (OFDMA), or Multi-Carrier Code Division Multiple Access(MC-CDMA). The invention can be applied to either Time DivisionDuplexing (TDD) or Frequency Division Duplexing (FDD). Without loss ofgenerality, OFDMA is therefore only used as an example to illustrate thepresent technology.

The following description provides specific details for a thoroughunderstanding of, and enabling description for, various embodiments ofthe technology. One skilled in the art will understand that thetechnology may be practiced without these details. In some instances,well-known structures and functions have not been shown or described indetail to avoid unnecessarily obscuring the description of theembodiments of the technology. It is intended that the terminology usedin the description presented below be interpreted in its broadestreasonable manner, even though it is being used in conjunction with adetailed description of certain embodiments of the technology. Althoughcertain terms may be emphasized below, any terminology intended to beinterpreted in any restricted manner will be overtly and specificallydefined as such in this Detailed Description section.

I. Wireless Communication Network

FIG. 1 is a representative diagram of a wireless communication network100 that services a geographic region. The geographic region is dividedinto a plurality of cells 102, and wireless coverage is provided in eachcell by a base station (BS) 104. One or more mobile devices (MS) 108 maybe fixed or may roam within the geographic region covered by thenetwork. The mobile devices are used as an interface between users andthe network. Each base station is connected to the backbone of thenetwork, usually by a dedicated link. A base station serves as a focalpoint to transmit information to and receive information from the mobiledevices within the cell that it serves by radio signals. Note that if acell is divided into sectors 106, from a system engineering point ofview each sector can be considered as a cell. In this context, the terms“cell” and “sector” are interchangeable.

In a wireless communication system with base stations and mobiledevices, the transmission from a base station to a mobile device iscalled a downlink (DL) and the transmission from a mobile device to abase station is called an uplink (UL). FIG. 2 is a block diagram of arepresentative transmitter 200 and receiver 220 that may be used in basestations and mobile devices to implement a wireless communication link.The transmitter comprises a channel encoding and modulation component202, which applies data bit randomization, forward error correction(FEC) encoding, interleaving, and modulation to an input data signal.The channel encoding and modulation component is coupled to a subchanneland symbol construction component 204, an inverse fast Fourier transform(IFFT) component 206, a radio transmitter component 208, and an antenna210. Those skilled in the art will appreciate that these componentsconstruct and transmit a communication signal containing the data thatis input to the transmitter 200. Other forms of transmitter may, ofcourse, be used depending on the requirements of the communicationnetwork.

The receiver 220 comprises an antenna 234, a reception component 232, aframe and synchronization component 230, a fast Fourier transformcomponent 228, a frequency, timing, and channel estimation component226, a subchannel demodulation component 224, and a channel decodingcomponent 222. The channel decoding component de-interleaves, decodes,and derandomizes a signal that is received by the receiver. The receiverrecovers data from the signal and outputs the data for use by the mobiledevice or base station. Other forms of receiver may, of course, be useddepending on the requirements of the communication network.

FIG. 3 depicts the basic structure of a multi-carrier signal in the timedomain, which is generally made up of time frames 300, subframes 302,time slots 304, and OFDM symbols 306. A frame consists of a number oftime slots, and each time slot is comprised of one or more OFDM symbols.The OFDM time domain waveform is generated by applying aninverse-fast-Fourier-transform (IFFT) to the OFDM signals in thefrequency domain. A copy of the last portion of the time waveform, knownas the cyclic prefix (CP) 308, is inserted in the beginning of thewaveform itself to form the OFDM symbol. In the case of TDD, guardperiods (GP1 310 and GP2 312), are inserted between an uplink (UL)subframe and a downlink (DL) subframe and between a DL subframe and a ULsubframe to account for the time needed to turn on and off transmittersand receivers, as well as radio propagation delay.

II. Multiple-Antenna System for Cellular Communication and Broadcasting

In cellular communications, different types of transmission modes may beused for different types of applications. When a base station sendsspecific data to an individual mobile station within its sector, thetransmission mode is referred to as unicast and when a base stationsends the same data to all mobile stations within its sector or cell,the transmission mode is referred to as broadcast. The multiple-antennasystem disclosed herein can be controlled, adjusted, configured, orreconfigured to produce desirable radiation patterns suitable fordifferent types of applications, such as unicast transmissions with aspecific reuse scheme or broadcast transmissions with one or morechannels.

Although a cell divided into three sectors is used as an example herein,those skilled in the art will appreciate that a cell may be divided intoan arbitrary number of sectors and that the disclosed technology is notlimited by the number of sectors within a cell.

A Cellular Communication and Broadcasting Transmissions

FIG. 4 depicts a transmitter 400 at a base station for cellularcommunication and broadcasting. The transmitter may consist of thefollowing subsystems:

-   -   1. baseband processors (BBPs) 404, which process digital data,        assembling or disassembling data payloads and formatting the        data in accordance with certain protocols as was previously        described with respect to FIG. 3;    -   2. intermediate frequency (IF) and radio frequency (RF)        transceivers (TRXs) 406 that are coupled to the baseband        processors 404 and which convert digital baseband signals from        the baseband processors into analog signals for transmission;    -   3. a signal distribution network 408 coupled to the RF/IF        transceivers 406, the signal distribution network receiving        signals from the RF/IF transceivers and splitting and/or        combining the signals in accordance with the requirements of        particular applications being served by the transmitter;    -   4. RF units (RFUs) 410 that are coupled to the signal        distribution network 408, the RF units amplifying the signals to        a certain power level for transmission; and    -   5. a multiple-antenna system 412 that is coupled to the RF units        410, the multiple-antenna system transmitting the signals with        various beam patterns (sectorial, omni-directional, etc.) in        accordance with a transmission mode that is selected based on        the frequency reuse scheme and the type of application. The        multiple-antenna system depicted in FIG. 4 consists of three        sector-antennas, the radiation pattern of each sector-antenna        which is fan-shaped. Alternatively, the system may consist of an        omni-directional antenna, the radiation pattern of which is        omni-directional in azimuth. In some embodiments, the system may        consist of both omni-directional antennas and sector antennas in        a particular combination. For example, antenna 1 in the        multiple-antenna system 412 may be an omni-directional antenna        and antennas 2 and 3 may be sector antennas.

Those skilled in the art will appreciate that the subsystems in thetransmitter 400 may be constructed with appropriate components anddevices, such as switches, amplifiers, and/or couplers. The subsystemsin the transmitter are controlled by a controller 402, which is coupledto each of the subsystems.

While the distribution network 408 is depicted between the RF/IFtransceivers 406 and RF units 410 in FIG. 4, those skilled in the artwill appreciate that the distribution network can be placed at variousother points in the transmitter 400. For example, the distributionnetwork can be placed between the antenna system 412 and RF units 410.Alternatively, as depicted in FIG. 5, if the functionality of the RF/IFtransceivers 406 is split into IF transceivers 502 and RF transceivers504, the distribution network 408 can be placed between the IF and RFtransceivers. In the reuse-3 case (that is, each cell is split intothree sectors and each sector uses a different frequency band forcommunication), f₁, f₂, and f₃ in FIG. 4 denote the three bands in RF orf_(IF1), f_(IF2), and f_(IF3) in FIG. 5 denote the three bands in IF. Inthe reuse-1 case, f₁, f₂, and f₃ represent the same RF channel orf_(IF1), f_(IF2), and f_(IF3) represent the same IF channel.

The signal distribution network 408, which consists of amplifiers,splitters, switches, and combiners, is used to distribute and adjustsignals so as to realize different settings or configurations requiredby various transmission modes to accommodate different applications.FIG. 6 depicts a typical implementation of the distribution network 408.Three signal paths through the distribution network are depicted, withthree inputs (1, 2, and 3) to the distribution network and three outputs(A, B, and C) from the distribution network. Those skilled in the artwill appreciate that the number of inputs to and outputs from thedistribution network can be varied depending on the desired transmissionmodes to be implemented. The gain on each path is controlled via acorresponding amplifier 602. The output from each amplifier is coupledto a splitter 604, which splits the output from the amplifier intomultiple signals. Each output from the splitter 604 is coupled to aswitch 606, which may be a simple ON-OFF control device. The output fromeach switch is coupled to a combiner 608. The splitters 604 perform thefunction of splitting (or fanning out) the input signal and thecombiners 608 perform the function of combining the input signals. Insome embodiments, the combiners may add the signals and operate over abroad range of frequencies. By selectively controlling the gain ofamplifiers 602 and the state of switches 606, the signals on outputs (A,B, and C) may be any combination of the signals received on inputs (1,2, 3). Additional filtering or signal conditioning (not shown) may beimplemented in the signal distribution network as well.

Those skilled in the art will appreciate that other configurations ofcomponents can used to achieve the same functionality as is implementedby distribution network 408. For example, the combination of anamplifier, a splitter, and switches identified by reference numeral 610in FIG. 6 can be replaced by one of the variations shown in FIGS. 7A and7B. In FIG. 7A, switches 606 are replaced by a switch 700 that eitherdirectly connects the amplifier 602 to the combiner, or connects theamplifier to the splitter 604. In FIG. 7B, switches 606 are replaced bya coupler 704 and a switch 706 that allows the amplifier 602 to bedirectly connected to the combiner, or connected to the splitter 604.

Various types of transmissions can be carried out by controlling theamplification provided by the amplifiers and the state of the switches.For example, to enable unicast transmission, switches 1, 5, and 9 areturned on and switches 2, 3, 4, 6, 7, and 8 are turned off. When theswitches are in this state, the signals received on inputs (1, 2, 3) ofthe distribution network are directly coupled to the outputs (A, B, C)of the distribution network. Referring to FIG. 4, if the signal flow fora sector 1 transmission were to be followed, the signals would flow fromthe baseband processor BBP1 through the distribution network to RFU Aand antenna 1.

To enable broadcast transmission using only one channel but three sectorantennas, only the switches connected to a particular splitter (forexample, switches 1, 2, and 3) are turned on and the rest of theswitches (in this example, 4, 5, 6, 7, 8, and 9) are turned off. Signalsgenerated by a particular BBP (BBP1) are thereby transmitted via allthree antennas while other BBPs (BBP2 and BBP3) are not transmitted.

To enable broadcast transmission using two channels but three sectorantennas, only the switches connected to a particular splitter (forexample, switches 7, 8, and 9) are turned off and the rest of theswitches (in this example, 1, 2, 3, 4, 5, and 6) are turned on. Signalsgenerated by the two BBPs (BBP1 and BBP2) are thereby transmitted viaall three antennas while the other BBP (BBP3) is not transmitted.

Turning on all switches enables broadcast transmission using threechannels and three sector antennas. That is, signals generated by anyBBP are transmitted via all three sector antennas. Some typical examplesof transmission modes are listed in Table 1 with their correspondingswitch states. A configuration index is provided in Table 1 todistinguish the different transmission modes and enable quick look-up ofconfiguration information as will be described in additional detailbelow.

TABLE 1 Schemes of frequency reuse and types of transmission and theircorresponding configuration index and settings Frequency reuseConfiguration and type of ON OFF Gain Elevation Index transmissionswitches switches settings beam 1 Unicast 1, 5, 9 2, 3, 4, Amp 1 = x1Conformed 6, 7, 8 Amp 2 = y1 Amp 3 = z1 2 Broadcast using 1, 2, 3 4, 5,6, Amp 1 = x2 Extended one channel 7, 8, 9 Amp 2 = y2 Amp 3 = z2 3Broadcast using 1, 2, 3, 7, 8, 9 Amp 1 = x3 Extended two channels 4, 5,6 Amp 2 = y3 Amp 3 = z3 4 Broadcast using 1, 2, 3, N/A Amp 1 = x4Extended all channels 4, 5, 6, Amp 2 = y4 7, 8, 9 Amp 3 = z4

While Table 1 represents many of the most common transmission modes,other combinations of the switch states can be employed to enabletransmissions for specific applications. For example, with switches 1,2, 4, 5, and 9 on and the rest of the switches off, signals generated byBBP1 and BBP2 are transmitted using two channels in both Sector 1 andSector 2, whereas signals generated by BBP3 are only transmitted in itsown corresponding sector (i.e., Sector 3). The number of transmissionmodes is only limited by the construction of the signal distributionnetwork and antennas.

The switch configuration necessary to achieve a desired transmissionmode may also depend, in part, on the types of antennas used in themulti-antenna system 412. For example, if antenna 1 in themultiple-antenna system 412 is an omni-directional antenna and antennas2 and 3 are sector antennas, a broadcast transmission mode can beenabled using only the omni-directional antenna. With switch 1 turnedon, signals from BBP1 (one channel) are transmitted through antenna 1.With switches 1 and 4 turned on, signals from both BBP1 and BBP2 (twochannels) are transmitted through antenna 1. With switches 1, 4, and 7turned on, signals from all BBPs (three channels) are transmittedthrough antenna 1.

In other embodiments, the gain setting on each path is set according toa specific scheme of frequency reuse and a specific type of transmissionby the adjustable amplifier.

B Controllable Beam Patterns for Cellular Communication and Broadcasting

By shaping the azimuth beam patterns and activating a predefinedelevation beam pattern, different radiation beam patterns are generatedby the antennas for transmissions in different types of applications.For example, FIG. 8 depicts the radiation beam pattern of a cell sectorantenna as viewed from overhead. As depicted in FIG. 8, a narrow beam806 in azimuth is used for unicast; a sector-specific beam 804 is usedfor broadcast transmissions within the cell; and a broadcast beam 806 isused for multi-cell broadcast transmissions. FIG. 9 depicts theradiation beam pattern of a cell sector antenna as viewed in elevation.As shown in FIG. 9, an elevation beam 904 that is conformed within acell boundary is used for unicast and sector-specific broadcast, whereasan elevation beam 902 that extends beyond the cell boundary is used formulti-cell broadcast.

FIGS. 10A and 10B are each examples of an antenna system 412 that arecontrollable in azimuth and elevation, and are suitable for operating indifferent transmission modes in cellular communication and broadcasting.The antennas depicted in FIGS. 10A and 10B possess the followingattributes:

-   -   1. the antenna consists of a plurality of antenna elements that        can be controlled individually or collectively; and    -   2. the azimuth pattern and elevation pattern of the antenna can        be shaped independently.        The antenna system depicted in FIG. 10A is a 2-dimensional        antenna systems 1000, meaning that the antenna elements 1002 are        mounted in an array on a substrate 1004 that orients the antenna        elements in roughly a plane. One or more antenna systems 1000        may be mounted in a desired configuration in order to transmit        within a particular region. For example, six of the antenna        systems may be deployed in a regular hexagon shape in order to        provide 360 degrees of coverage to a cell. In contrast, the        antenna system depicted in FIG. 10B is a 3-dimensional antenna        system 1020, meaning that the array of antenna elements 1002 are        mounted on a substrate that orients the antenna elements in        various directions. The substrate 1024 in FIG. 10B is a        cylindrical substrate, creating an antenna capable of generating        a 360 degree radiation pattern.

The azimuth beam pattern and the elevation beam patterns of the antennasystems in FIGS. 10A and 10B may be shaped in a variety of ways. Withrespect to the azimuth pattern, one or more beamformers 1022 may becoupled between the RF units (which provide RF signal feeds) and theantenna systems. The beamformers may be controlled by the controller402. Those skilled in the art will appreciate that beamformers controlthe amplitude and phase of a signal at each transmitter, in order tocreate a pattern of constructive and destructive interference thatcontrols the directionality of the radiation pattern emitted by theantennas. The azimuth patterns can be defined, either in a digital oranalog manner, by the signal weights to the antennas. In general, theweights are applied in either time or frequency domain. In the case ofOFDMA, the weights are applied to the corresponding subcarriers in thefrequency domain within the beamformers 1106, as shown in FIG. 11.

With respect to the elevation beam pattern, a desired beam pattern canbe achieved by controlling how antenna elements 1002 are activated bythe system. FIG. 12 depicts two representative antenna elements 1002,such as might be fixed to an antenna substrate. The antenna elementscomprise one or more electronic circuits 1202 that are surrounded byradiation elements 1204. By activating some or all of the electroniccircuits 1202, the resulting emitted radiation beam may be adjusted inelevation. Certain elevation beam patterns may be predefined and can beactivated, individually or in combination, by the antenna controller.

It will be appreciated that in certain applications of beamforming,transmit-diversity, or multiple-input-multiple-output (MIMO)transmissions in azimuth, the transmitter 400 design (includingdistribution network 408) may be modified to accommodate greater antennacomplexity. FIG. 13 is a block diagram of a parallel transmitterconstruction for such an application. Specifically, the transmitter ismodified to generate N outputs from each BBP, where N corresponds to thenumber of antenna subsystems in the azimuth dimension or to the numberof azimuth beams need to cover a desired area (e.g., a sector). Theoutputs from the BBPs are coupled to an array of RF transceivers 1302, abank of N distribution networks 1304, and an array of RF Units 1306.Outputs from the transmitter with a parallel construction are coupled tothe antenna system and used for beamforming, transmit-diversity, or MIMOtransmission.

The transmitter and antenna constructions disclosed herein enable themultiple-antenna system to switch between a variety of transmissionmodes that are suitable for different applications, such as audio,video, voice, etc. In one transmission mode, unicast data such asuser-specific data and pilot subcarriers are transmitted to MSs by theirserving BS using narrow beams (adaptively shaped or otherwise) ororthogonal beams in azimuth. Adaptive modulation and coding, as well aspower control, can be jointly applied with these unicast-shaped beams.

In another transmission mode, sector-specific data and pilot subcarriersare transmitted to MSs by their serving BS using a shaped beam thatcovers its designated sector in azimuth. Signals that are associated thesector-specific data subcarriers include preamble, mid-amble, framecontrol header, downlink resource allocation, uplink resourceallocation, or any information that is required to be disseminated tothe MSs within the sector covered by the serving BS. Since thedirectivity gain of a sector beam is typically smaller than a narrowbeam in the unicast case, a relatively robust modulation and codingscheme may be used for a sector-specific broadcast with a sector-shapedbeam.

In still another transmission mode, broadcast data and pilot subcarriersare transmitted by a BS using a beam pattern that is shaped in bothelevation and azimuth to maximize the network coverage. For example, inthe same frequency network (SFN), it is desirable that the beam patternof a BS should, to a certain degree, overlap in both azimuth andelevation with others, so as to achieve the optimal effects ofmacro-diversity. The gain from the macro-diversity should be able tooffset, to a certain extent, the link-budget imbalance as compared tothe sector beam case and narrow beam case.

The combination of a particular scheme of frequency reuse and a specifictype of transmission can be represented by a configuration index, suchas the configuration index represented in column 1 of Table 1. Forexample, an instruction to or from the controller 402 to modify thetransmission mode may be in the form of the configuration index. Thecontroller may use a look-up table or other data construct to determinethe appropriate switch 606 settings and amplifier 602 gain settings thatare associated with the specified configuration index, as exemplified inTable 1. In addition, the configuration index may also dictate the typeof elevation beam used for a specific transmission (e.g., “conformed” or“extended” in Table 1). Given a configuration index, the controller willcontrol the gain, switch setting, and beamformer or other antennacontrol to produce a desired beam pattern for transmission or reception.

In some embodiments, mechanisms are employed to deal with the transitionfrom one transmission mode to another transmission mode. In particular,a transition period (TP) may be inserted between transmission slots ofdifferent types of applications. For example, in the time structureshown in FIG. 3, DL Slot #1 may be a video broadcast slot and DL Slot #2may be a data unicast slot. FIG. 14 is a block diagram depicting how theDL subframe 302 may be modified to incorporate a transition period. Asdepicted in FIG. 14, a transition period 1404 is inserted between avideo broadcast slot 1402 and a data unicast slot 1406. The transitionfrom one type of application to the next may require turning on/offswitches and/or amplifiers, antenna control circuits, etc. The TP thatis inserted must be sufficiently long for these devices to reach steadyor near steady states. In addition, necessary MAC functions dealing withthe TP such as scheduling and control messages will be performed by theMAC processor. It will be appreciated that the length of the transitionperiod may be a constant that is selected based on the worst-case amountof time necessary for devices to reach steady or near steady state whenswitching from one transmission mode to another transmission mode.Alternatively, the length of the transition period may be varied so thatit is optimized depending on the type of transition between transmissionmodes.

Instead of inserting a transition period to accommodate a switch fromone transmission mode to another transmission mode, the transition canbe scheduled to take place between OFDM symbols such that a portion ofthe cyclic prefix or postfix can be used for the switched devices toreach a steady or near-steady state, provided that the cyclic prefix orpostfix is designed to be longer than the time required for thetransition.

The above detailed description of embodiments of the system is notintended to be exhaustive or to limit the system to the precise formdisclosed above. While specific embodiments of, and examples for, thesystem are described above for illustrative purposes, various equivalentmodifications are possible within the scope of the system, as thoseskilled in the relevant art will recognize. For example, while processesare presented in a given order, alternative embodiments may performroutines having steps in a different order, and some processes may bedeleted, moved, added, subdivided, combined, and/or modified to providealternative or subcombinations. Each of these processes may beimplemented in a variety of different ways. Further any specific numbersnoted herein are only examples: alternative implementations may employdiffering values or ranges.

These and other changes can be made to the invention in light of theabove Detailed Description. While the above description describescertain embodiments of the technology, and describes the best modecontemplated, no matter how detailed the above appears in text, theinvention can be practiced in many ways. Details of the system may varyconsiderably in its implementation details, while still beingencompassed by the technology disclosed herein. As noted above,particular terminology used when describing certain features or aspectsof the technology should not be taken to imply that the terminology isbeing redefined herein to be restricted to any specific characteristics,features, or aspects of the technology with which that terminology isassociated. In general, the terms used in the following claims shouldnot be construed to limit the invention to the specific embodimentsdisclosed in the specification, unless the above Detailed Descriptionsection explicitly defines such terms. Accordingly, the actual scope ofthe invention encompasses not only the disclosed embodiments, but alsoall equivalent ways of practicing or implementing the invention underthe claims.

We claim:
 1. A transmission method for a base station in a cell of anorthogonal frequency division multiplexing (OFDM) wireless system, themethod comprising: selecting a plurality of cell-specific OFDMsubcarriers in a time slot for transmission to mobile devices within thecell, wherein a first weight is applied to a cell-specific OFDMsubcarrier; selecting a plurality of user-specific OFDM subcarriers inthe time slot for transmission to a specific mobile device within thecell, wherein a second weight is applied to a user-specific OFDMsubcarrier; transmitting control information on the plurality ofcell-specific OFDM subcarriers through a first group of antennas; andtransmitting user-specific data on the plurality of user-specific OFDMsubcarriers through a second group antennas; wherein the first group ofantennas produce a first beam pattern having a first azimuth pattern andfirst elevation pattern, and the second group of antennas produce asecond beam pattern having a second azimuth pattern and second elevationpattern, and wherein the first beam pattern is different than the secondbeam pattern in either azimuth pattern or an elevation pattern.
 2. Themethod of claim 1, wherein the plurality of cell-specific OFDMsubcarriers comprise cell-specific data OFDM subcarriers andcell-specific pilot OFDM subcarriers.
 3. The method of claim 1, whereinthe plurality of user-specific OFDM subcarriers comprise user-specificdata OFDM subcarriers and user-specific pilot OFDM subcarriers.
 4. Themethod of claim 1, further comprising dividing a transmission timeperiod into a plurality of frames, wherein each frame contains aplurality of subframes, each subframe contains a plurality of timeslots, and each time slot contains a plurality of OFDM symbols.
 5. Themethod of claim 1, wherein the control information includes downlink oruplink resource allocation information.
 6. The method of claim 1,wherein the control information and the user-specific data are modulatedwith different modulation and coding schemes.
 7. A base station in acell of an orthogonal frequency division multiplexing (OFDM) wirelesssystem, the base station comprising: a controller configured to: selecta plurality of cell-specific OFDM subcarriers in a time slot fortransmission to mobile devices within the cell, wherein a first weightis applied to a cell-specific OFDM subcarrier; and select a plurality ofuser-specific OFDM subcarriers in the time slot for transmission to aspecific mobile device within the cell, wherein a second weight isapplied to a user-specific OFDM subcarrier; and a transmitter configuredto: transmit control information on the plurality of cell-specific OFDMsubcarriers through a first group of antennas; and transmituser-specific data on the plurality of user-specific OFDM subcarriersthrough a second group antennas; wherein the first group of antennasproduce a first beam pattern having a first azimuth pattern and firstelevation pattern, and the second group of antennas produce a secondbeam pattern having a second azimuth pattern and second elevationpattern, and wherein the first beam pattern is different than the secondbeam pattern in either an azimuth pattern or an elevation pattern. 8.The base station of claim 7, wherein the transmitter comprises a channelencoding component, a modulation component, and an inverse fast Fouriertransform (IFFT) component.
 9. The base station of claim 7, wherein atransmission time period is divided into a plurality of frames and eachframe contains a plurality of subframes, each subframe contains aplurality of time slots, and each time slot contains a plurality of OFDMsymbols.
 10. The base station of claim 7, wherein the controlinformation includes downlink or uplink resource allocation information.11. The base station of claim 7, wherein the control information and theuser-specific data are modulated with different modulation and codingschemes.